1-Alkyl-3-methylimidazolium Bis(perfluoroalkylsulfonyl)imide Water-Immiscible Ionic Liquids : The Effect of Water on Electrochemical and Physical Properties

Abstract

The electrochemical and physical properties of a class of 1-n-alkyl-3-methylimidazolium bis(perfluoroalkylsulfonyl)imide room-temperature ionic liquids (RTILs) is reported. By varying the chain length on the cation 8, and 10) and the perfluorinated carbon chains of the imide anions, (BMSI) to (BETI), the effect on water content, viscosity, conductivity, and potential window has been examined. The water content of the RTILs, both ambient and water-equilibrated, varies linearly with the imidazolium alkyl chain length. The viscosities of the water-equilibrated BMSI- and BETI-based RTILs were accurately calculated using a linear combination of the viscosity of water and the ambient RTILs. The conductivities for this series ranges from 2.9 mS/cm to 0.92 mS/cm and were accurately estimated based on the viscosity, density, and molecular weight. The potential windows of the ambient RTILs are 4.3 and 4.9 V for the BMSI and BETI salts, respectively. The window is reduced to 3.9 and 4.3 V upon equilibration with water. The reversible electrochemistry of ferrocene and decamethylferrocene has been measured in water-equilibrated imide-based RTILs with as much as 23 mol% © 2004 The Electrochemical Society. All rights reserved.